CMOS image sensors are electrical solid-state imaging sensors, which are exhibiting more superiority in the aspects of system complexity and reliability, data output and exposure control, etc., than traditional CCD, due to their intrinsic high integration. Therefore, audio and video products based the CMOS image sensors will replace the CCD products to become the main trend of market in the future.
In the semiconductor manufacturing process, the CMOS image sensors proposes special requirements for structures of their shallow trenches. In addition to having active regions as the traditional CMOS, pixel regions are also required to manufacture to meet the needs of image sensor. Therefore, in the shallow trench etching process, two different etch depths are required to form two kinds of active regions structure.
Referring to FIGS. 1-5, which are schematic views illustrating a shallow trench forming process at the dual active regions of the prior art. As shown in FIGS. 1-5, the solutions of the prior art are that adopting two separate photoresist exposure processes to meet the shallow trench etching's needs of different depths at the active regions I and the pixel regions II of the CMOS image sensors respectively. Detailed steps are as follows:
1) using a first accurate photomask to accomplish the exposure of active regions I of the CMOS image sensors, as shown in FIG. 1;
2) accomplishing a shallow trench etching process with required depth for active regions I of the CMOS image sensors in the etching process chamber, as shown in FIG. 2;
3) adopting subsequent a stripping process and a cleaning process to remove polymer residues generated by the reaction;
4) using a second accurate photomask to accomplish the exposure of the pixel regions II, as shown in FIG. 3;
5) accomplishing a shallow trench etching process with required depth for the pixel regions II in the etching process chamber, as shown in FIG. 4;
6) adopting subsequent a stripping process and a cleaning process to remove the polymer residues generated by the reaction. Finally, the shallow trench structure with different depths at the dual active regions is formed, as shown in FIG. 5.
However, above solutions of the prior art exist some problems, which are:
1) the two accurate photomasks are needed which increases the cost;
2) the shallow trench depths at the active regions of the CMOS image sensors after the first etching process will bring great difficulties for the refilling ability and flatness of the BARC layer 1 (bottom anti-reflective coating) of the second accurate photomask.